1. Technical Field
This disclosure relates to multiple photovoltaic strings, which have direct current (DC) outputs, which are interconnected at an input of a power combiner junction box and specifically to a system and method to disconnect and or connect a photovoltaic string DC output from the input of the power combiner junction box.
2. Description of Related Art
In a photovoltaic distributed power harvesting system, a photovoltaic string includes a series connection of photovoltaic panels. Photovoltaic strings may be connected in parallel to give a parallel direct current (DC) power output. The parallel DC power output may connect to the input of a direct current (DC) to an alternating current (AC) inverter. The AC power output of the inverter connects across an AC load. The load may be an AC load such as an AC motor or may be an electrical power grid.
A Residual-Current Circuit Breaker (RCCB) is an electrical wiring device that disconnects a circuit whenever it detects that the electric current is not balanced between the energized conductor and the return neutral conductor. Such an imbalance may indicate current leakage through the body of a person who is grounded and accidentally touching the energized part of the circuit. A lethal shock can result from these conditions. RCCBs are designed to disconnect quickly enough to prevent injury caused by such shocks. They are not intended to provide protection against overcurrent (overload) or short-circuit conditions.
In the United States and Canada, a residual current device is most commonly known as a ground fault circuit interrupter (GFCI), ground fault interrupter (GFI) or an appliance leakage current interrupter (ALCI). In Australia they are sometimes known as “safety switches” or simply “RCD” and in the United Kingdom, along with circuit breakers, they can be referred to as “trips” or “trip switches.”
Under some circumstances, such as in a photovoltaic distributed power harvesting system, a residual current may also represent a fire hazard.
Thus, there is a need for and it would be advantageous to have a system and method for disconnection of a photovoltaic string carrying direct current power when residual current is detected in the photovoltaic string to prevent fire hazards in photovoltaic arrays.